1. Field of the Invention
The invention generally relates to a structure and a method for forming an integrated circuit chip carrier structure and more particularly to an integrated circuit chip mounted on a chip carrier with a set of compressible support members that transmit force from a thermally conductive device to the chip carrier.
2. Description of the Related Art
High power electronic devices are often cooled by bonding them to a good thermal conductor. In common configurations, this is accomplished by first joining the front (circuit) side of a flip chip to a substrate or carrier using electrical conductors (e.g., solder balls). A thermal conductor (a heat spreader or heatsink) is then bonded to the back side of the die using curable organic materials or a solder. In either case, the gap between the die and the thermal conductor should be made as thin as possible to minimize the thermal resistance path without impacting the thermal reliability of the structure.
There are several types of LGA interposers in the market. What they have in common is that they have features that align the interposer to the substrate (chip carrier) and features that aligns the interposer to the card/board, and they have a means of keeping the array of electrical contacts in alignment. They types of contacts vary widely, from springs, to organics, to types of buttons. Each of these types of interposers has some minimum load that is required at each contact to achieve and maintain the required electrical performance. The higher the minimum load, the higher the total required load, the more challenging (and sometimes costly) the solution becomes.
In many cases, the substrate is connected to other components (e.g., board, mothercard, etc.) using a compressive load. This load may serve to physically position and electrically connect the substrate to other components (i.e., using an LGA, land grid array interposer). Ideally, the load is applied uniformly on the substrate using the contact area of the chip. However, for designs in which the die is substantially smaller in area than the substrate, placing a load onto the die to affect a compressive load can cause deformation of the substrate, stress in the thermal interface adhesive, stress in the chip and solder interconnections, highly non-uniform LGA loading, and failure of the assembly. The more uniform that load can be generated, the lower the total load is. Some of the design options for generating uniform loads are the means that the load is applied to the chip carrier, the stiffness of that carrier (thickness and material selection), and the stiffness of the backing plate (thickness and material selection). The invention described below provides a solution to this problem by utilizing structures that distributed the load being imparted by the heatsink partially to the chip and partially to the chip carrier.